1. Technical Field
The present invention relates to a method for etching a laminate film laminated a plurality of conductive films and to a method for manufacturing a semiconductor device using such conductive films.
2. Background Art
Recently, development of display devices have been getting more and more active, and miniaturization of individual elements constituting the display devices has been desired.
For miniaturization of an element, a high-accuracy etching technique is necessary. Typically, an electrode or a wiring is formed by forming a conductive film and by wet etching or dry etching. However, dry etching is more suitable for forming a minute structure (refer to Japanese Patent No. 2734753, Japanese Patent Laid-Open No. 2001-188240, and Japanese Patent Laid-Open No. 2003-174173).
For this element, a low-resistance conductive film, for example, a conductive film including aluminum (Al) as its main component is used as a material for forming an electrode or a wiring. It is often the case that a gas including chlorine, such as Cl2, BCl3, SiCl4, or CCl4, is used for dry etching of aluminum.
Now, it is often the case that a transparent conductive film is provided in a pixel portion of a display device, and an electrode is formed by laminating a transparent conductive film and a low-resistance conductive film as described above in order to decrease the resistance and improve contact with an element such as a thin film transistor. However, it has been found that, during etching of the transparent conductive film by dry etching, an etching gas reacts with the conductive film to produce fine particles.
In FIG. 2(A) and FIG. 2(B), reference numeral 1001 denotes an indium tin oxide alloy (Indium Tin Oxide (ITO)) film that is a transparent conductive film, and reference numeral 1002 denotes an aluminum film (Al film). After forming the Al film 1002 on the ITO film 1001 (FIG. 2(A)), the Al film 1002 is etched. However, when a chlorine-based gas, for example, a mixed gas of BCl3 and Cl2, is used as the etching gas, the ITO film 1001 reacts with chlorine (Cl) in the mixed gas to form fine particles 1003 on the periphery of the etched region while the Al film is etched (FIG. 2(B)).
In addition, FIG. 3(A) and FIG. 3(B) show an example in which a titanium film (Ti film) is formed between an ITO film and an Al film. Reference numerals 1101, 1102, and 1103 denote the ITO film, the Ti film, and the Al film (FIG. 3(A)). However, when the Al film 1103 and the Ti film 1102 are continuously etched with a gas including chlorine, for example, a mixed gas of BCl3 and Cl2, as an etching gas, the ITO film 1101 formed under the Ti film 1102 is exposed, and chlorine (Cl) reacts with the ITO film 1101. The result is that fine particles 1104 are produced as in FIG. 2(B) (FIG. 3(B)).
These particles cause a short circuit between the transparent conductive film and other conductive film, and for example, cause a point defect or a line defect in a pixel portion when a display device is manufactured.